Semiconductor structure and manufacturing method therefor

ABSTRACT

Embodiments of the present application provide a semiconductor structure and a manufacturing method therefor. A buffer layer is disposed on a substrate layer, and the buffer layer includes a first buffer layer and a second buffer layer. By doping a transition metal in the first buffer layer, a deep level trap may be formed to capture background electrons, and diffusion of free electrons toward the substrate may also be avoided. By decreasing a doping concentration of the transition metal in the second buffer layer, a tailing effect is avoided and current collapse is prevented. By doping periodically the impurity in the buffer layer, the impurity may be as an acceptor impurity to compensate the background electrons, and then a concentration of the background electrons is reduced. By using the periodic doping method, dislocations, caused by doping, in the buffer layer may be effectively reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of International ApplicationNo. PCT/CN2019/074396 filed on Feb. 1, 2019, the entire contents ofwhich are incorporated herein by reference.

TECHNICAL FIELD

Embodiments of the present application relate to the field ofmicroelectronic technologies, in particular to a semiconductor structureand a manufacturing method therefor.

BACKGROUND

High Electron Mobility Transistor (HEMT) is a kind of heterojunctionfield effect transistor. Taking AlGaN/GaN HEMT as an example, since aband gap of AlGaN is greater than that of GaN, two-Dimensional ElectronGas (2DEG) is formed at an interface between AlGaN and GaN if aheterojunction is formed by AlGaN and GaN. Therefore, HEMT is also knownas 2DEG field effect transistor.

As for GaN-based HEMTs, if other impurities or a transition metal suchas iron is doped into a region located below the 2DEG, a pinch-offcharacteristic may be improved, or a cut-off voltage may be increased.However, electrons trapped by charge traps formed by an impurity mayhinder formation of the 2DEG, thus being prone to current collapse.Although reducing a doping concentration of the impurity is beneficialto suppress the current collapse, the current collapse cannot be alsoeliminated if a thickness of a buffer layer is not adjusted accurately.

SUMMARY

In view of this, a semiconductor structure and a manufacturing methodtherefor are provided to suppress leakage current, improve a pinch-offcharacteristic of a device and avoid current collapse. Therefore, theleakage current of the device with the semiconductor structure may bebalanced in dynamic characteristics.

A semiconductor structure is provided according to an embodiment of thepresent application. The semiconductor structure includes a substrateand a buffer layer disposed on the substrate. The buffer layer includesa first buffer layer and a second buffer layer upward from the substratein turn. The first buffer layer is co-doped with a transition metal andan impurity. A doping concentration of the transition metal remainsconstant, and a doping concentration of the impurity is modulatedperiodically. A doping concentration of the transition metal is not lessthan a peak value of the doping concentration of the impurity in thefirst buffer layer. The second buffer layer is doped with the transitionmetal. A doping concentration of the transition metal in the secondbuffer layer is less than the doping concentration of the transitionmetal in the first buffer layer.

Further, in an embodiment of the present application, the dopingconcentration of the transition metal in the second buffer layerdecreases along a direction away from the substrate.

Further, in an embodiment of the present application, the semiconductorstructure further includes an impurity co-doped in the second bufferlayer. The doping concentration of the transition metal is not less thana doping concentration of the impurity in an upper surface of the secondbuffer layer. The upper surface of the second buffer layer is a surfaceof the second buffer layer away from the substrate.

Further, in an embodiment of the present application, the semiconductorstructure further includes a nucleating layer disposed between thesubstrate and the buffer layer.

A manufacturing method for a semiconductor structure is further providedin the present application. The manufacturing method includes providinga substrate and forming a buffer layer on the substrate. The bufferlayer includes a first buffer layer and a second buffer layer upwardfrom the substrate in turn. The first buffer layer is co-doped with atransition metal and an impurity. A doping concentration of thetransition metal remains constant, and a doping concentration of theimpurity is modulated periodically. The doping concentration of thetransition metal is not less than a peak value of the dopingconcentration of the impurity in the first buffer layer. The secondbuffer layer is doped with the transition metal. The dopingconcentration of the transition metal in the second buffer layer is lessthan the doping concentration of the transition metal in the firstbuffer layer.

Further, in an embodiment of the present application, the dopingconcentration of the transition metal in the second buffer layerdecreases along a direction away from the substrate.

Further, in an embodiment of the present application, the manufacturingmethod for the semiconductor structure further includes doping animpurity in the second buffer layer. The doping concentration of thetransition metal is not less than a doping concentration of the impurityin an upper surface of the second buffer layer. The upper surface of thesecond buffer layer is a surface of the second buffer layer away fromthe substrate.

Further, in an embodiment of the present application, the manufacturingmethod for the semiconductor structure further includes forming anucleating layer between the substrate and the buffer layer.

The present application provides the semiconductor structure and themanufacturing method therefor. The buffer layer is disposed on thesubstrate layer, and the buffer layer includes the first buffer layerand the second buffer layer. By doping the transition metal in the firstbuffer layer, a deep level trap may be formed to capture backgroundelectrons, and diffusion of free electrons toward the substrate may alsobe avoided. By decreasing the doping concentration of the transitionmetal in the second buffer layer, a tailing effect is avoided andcurrent collapse is prevented. By doping periodically the impurity inthe buffer layer, the impurity may be as an acceptor impurity tocompensate the background electrons, and then a concentration of thebackground electrons is reduced. By using the periodic doping method,dislocations caused by doping, in the buffer layer may be effectivelyreduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic structural diagram of a semiconductor structureaccording to an embodiment of the present application.

FIG. 2a-2h show doping modes of doping concentrations of a transitionmetal and an impurity changed relative to a thickness in a semiconductorstructure according to the present application.

FIG. 3 shows a schematic structural diagram of a semiconductor structureaccording to another embodiment of the present application.

FIG. 4 shows a schematic structural diagram of a HEMT device configuredwith a semiconductor structure according to an embodiment of the presentapplication.

FIG. 5 shows a doping mode of doping concentrations of a transitionmetal and an impurity in the HEMT device shown in FIG. 4.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present application will be described in detail below in combinationwith specific embodiments shown in drawings. However, the presentapplication may not be limited by the embodiments. Changes in structure,method or function made by those skilled in the art based on theembodiments are all included in the protection scope of the presentapplication.

In addition, repeated labels or marks may be used in differentembodiments. These repetitions are only for describing the presentapplication briefly and clearly, instead of representing any correlationbetween the different embodiments and/or structures.

As shown in FIG. 1, a manufacturing method for a semiconductor structureincludes providing a substrate 1 and forming a buffer layer 3 on thesubstrate 1. The buffer layer 3 includes a first buffer layer 31 and asecond buffer layer 32 upward from the substrate in turn.

In the embodiment, the substrate 1 is made of at least one ofsemiconductor materials, ceramic materials and polymer materials. Forexample, the substrate 1 is made of at least one of sapphire, siliconcarbide, silicon, lithium niobate, Silicon On Insulator (SOI), galliumnitride and aluminum nitride.

The first buffer layer 31 is co-doped with a transition metal and animpurity. A doping concentration of the transition metal remainsconstant, and a doping concentration of the impurity is periodicallymodulated.

In the embodiment, a peak value of the doping concentration of theimpurity modulated periodically is not less than 1E17 cm⁻³, and a valleyvalue is not greater than 50% of the peak value. For example, the valleyvalue of the doping concentration of the impurity modulated periodicallyis not greater than 5E16 cm⁻³. Further, the valley value of the dopingconcentration of the impurity modulated periodically is not greater than3E16 cm⁻³. The impurity, in the first buffer layer 31, is used as anacceptor impurity to compensate background electrons introduced by otherimpurities (such as oxygen). Additionally, growth conditions such as lowpressure and low temperature are needed for achieving the high dopingconcentration of the impurity. However, a large number of dislocationsmay be introduced by the growth conditions. Therefore, the dislocationsof the buffer layer may be effectively reduced by doping the impurityperiodically.

Further, in the first buffer layer 31, the doping concentration of thetransition metal is not less than the peak value of the dopingconcentration of the impurity. The transition metal forms a deep leveltrap in the buffer layer to capture the background electrons.

Further, the second buffer layer 32 is doped with a transition metal. Adoping concentration of the transition metal in the second buffer layer32 is less than the doping concentration of the transition metal in thefirst buffer layer 31.

Further, the doping concentration of the transition metal in the secondbuffer layer 32 decreases along a direction away from the substrate 1,so as to avoid a tailing effect caused by the transition metal andprevent current collapse. A minimum doping concentration of thetransition metal in the second buffer layer 32 is not greater than 3E16cm⁻³, otherwise a deep level trap formed due to the excessively highdoping concentration of the transition metal may cause impurityscattering and reduce mobility.

Further, the semiconductor structure further includes an impurity dopedin the second buffer layer 32. In an upper surface of the second bufferlayer 32, the doping concentration of the transition metal is not lessthan a doping concentration of the impurity. The upper surface of thesecond buffer layer 32 refers to a surface of the second buffer layer 32away from the substrate 1.

Further, the transition metal mentioned above includes at least one ofTi, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ag and Cd, preferably, Fe. Theimpurity is C.

Further, a thickness of the first buffer layer 31 is 0.01 μm to 5 μm. Athickness of the second buffer layer 32 is 0.05 μm to 5 μm.

Specifically, as shown in FIG. 2 a, a horizontal axis represents athickness of the buffer layer 3. The upper surface of the second bufferlayer 32 is taken as 0 nm, and the closer to the substrate, the greaterthe thickness value represented by the horizontal axis is. A verticalaxis represents doping concentrations of doping atoms. In theembodiment, 0 nm to 600 nm in the horizontal axis refers to the secondbuffer layer 32, and 600 nm to 900 nm in the horizontal axis refers tothe first buffer layer 31. The first buffer layer 31 is doped with atransition metal Fe and an impurity C. A doping concentration of Feremains constant at 1E18 cm⁻³. A doping concentration of C is variedperiodically, a peak value of the doping concentration of C is 2E17 cm⁻³, and a valley value of the doping concentration of C is 2E16 cm⁻³.The second buffer layer 32 is doped without C, and a dopingconcentration of Fe gradually decreases to 2E16 cm⁻³.

Further, a doping concentration of C may remain constant in the secondbuffer layer 32. As shown in FIG. 2 b, the first buffer layer 31 isdoped with the transition metal Fe and the impurity C. The dopingconcentration of Fe remains constant at 1E18 cm⁻³. The dopingconcentration of C is varied periodically, and the peak value of thedoping concentration of C is 2E17 cm⁻³, the valley value of the dopingconcentration of C is 2E16 cm⁻³. The second buffer layer 32 is dopedwith the transition metal Fe and the impurity C. The dopingconcentration of Fe gradually decreases to 2E16 cm⁻³, and the dopingconcentration of C remains constant at 2E16 cm⁻³.

Further, the doping concentration of C may also be varied periodicallyin part of the second buffer layer 32. As shown in FIG. 2 c, the firstbuffer layer 31 is doped with the transition metal Fe and the impurityC. The doping concentration of Fe remains constant at 1E18 cm⁻³. Thedoping concentration of C is varied periodically. The peak value of thedoping concentration of C is 2E17 cm⁻³, and the valley value of thedoping concentration of C is 2E16 cm⁻³. The second buffer layer 32 isdoped with the transition metal Fe and the impurity C. The dopingconcentration of Fe gradually decreases to 2E16 cm⁻³. The dopingconcentration of C is varied periodically in part of the second bufferlayer 32, and the doping concentration of C remains constant at 2E16cm⁻³ in 0 nm to 350 nm. It may be understood that the second bufferlayer 32 is doped without C in 0 nm to 350 nm. A doping mode of C in thesecond buffer layer 32 is not limited, as long as the dopingconcentration of Fe is not less than the doping concentration of C nearthe upper surface of the second buffer layer 32 (that is, the uppersurface refers to the surface away from the first buffer layer 31).

Further, in the second buffer layer 32, decreasing slopes of the dopingconcentration of Fe is variable. As shown in FIG. 2 d, the first bufferlayer 31 is doped with the transition metal Fe and the impurity C. Thedoping concentration of Fe remains constant at 1E18 cm⁻³. The dopingconcentration of C is varied periodically. The peak value of the dopingconcentration of C is 2E17 cm⁻³, and the valley value of the dopingconcentration of C is 2E16 cm⁻³. In the second buffer layer 32, thedoping concentration of Fe decreases from 1E18 cm⁻³ at 600 nm to 9E17cm⁻³ at 500 nm, and then to 7E17 cm⁻³ at 300 nm, 5E17 cm⁻³ at 200 nm and3E17 cm⁻³ at 100 nm in turn, and finally to 2E16 cm⁻³ in the uppersurface of the second buffer layer 32.

It can be understood that a minimum doping concentration and thedecreasing slopes of the doping concentration of Fe in the second bufferlayer 32 may be affected by factors such as temperature of manufacturingenvironment, the thickness of the buffer layer, bond energy of the dopedtransition metal, diffusion activation energy of the doped buffer layer,the doping modes of metals, and dislocation density between the bufferlayer and the substrate layer. Therefore, a decreasing trends, adecreasing mode and a decreasing process of the doping concentration ofFe in the second buffer layer 32 are not specifically limited in thepresent application, as long as the doping concentration of Fe decreasesalong the direction away from the substrate, the decreasing trend andthe decreasing slopes increase larger and larger.

It can be understood that a doping period of the impurity C is notconstant. As shown in FIGS. 2a -2 d, doping of the impurity C takes athickness of 100 nm as a period. As shown in FIG. 2 e, the doping of theimpurity C takes a thickness of 50 nm as a period.

In the above embodiments, the doping concentration of the impurity C inthe buffer layer changes with the thickness to present a rectangularshape periodic modulation. In other embodiments, the dopingconcentration of the impurity C in the buffer layer changes with thethickness to present a periodic modulation of a trapezoid shape (asshown in FIG. 2f ) or a triangle shape (as shown in FIG. 2g ) or acombination thereof (as shown in FIG. 2h ). It can be understood thatthe shape presented by the periodic modulation is not limited in thepresent application, as long as the impurity in the first buffer layer31 is doped periodically.

Further, the described manufacturing method may be realized according toone or a combination of modes such as Atomic Layer Deposition (ALD),Chemical Vapor Deposition (CVD), Molecular Beam Epitaxy (MBE), PlasmaEnhanced Chemical Vapor Deposition (PECVD), Low Pressure Chemical VaporDeposition (LPCVD), Physical Vapor Deposition (PVD), Metal-OrganicMolecular Beam Epitaxy (MOMBE) and Metal-Organic Chemical VaporDeposition (MOCVD).

Further, as shown in FIG. 3, the manufacturing method for thesemiconductor structure further includes forming a nucleating layer 2between the substrate 1 and the buffer layer 3. The nucleating layer 2is made of one of AlN, GaN and AlGaN.

As shown in FIG. 3, a schematic diagram of a semiconductor structure isprovided according to an embodiment of the present application. Thesemiconductor structure includes a substrate 1 and a buffer layer 3disposed on the substrate 1. The buffer layer 3 includes a first bufferlayer 31 and a second buffer layer 32 upward from the substrate in turn.

The first buffer layer 31 is co-doped with a transition metal and animpurity. A doping concentration of the transition metal remainsconstant, and a doping concentration of the impurity is periodicallymodulated.

A peak value of the doping concentration of the impurity modulatedperiodically is not less than 1E17 cm⁻³, and a valley value is notgreater than 50% of the peak value. For example, the valley value of thedoping concentration of the impurity modulated periodically is notgreater than 5E16 cm⁻³. Further, the valley value of the dopingconcentration of the impurity modulated periodically is not greater than3E16 cm⁻³. The impurity, in the first buffer layer 31, is used as anacceptor impurity to compensate background electrons introduced by otherimpurities (such as oxygen). Additionally, growth conditions such as lowpressure and low temperature are needed for achieving the high dopingconcentration of the impurity. However, a large number of dislocationsmay be introduced by the growth conditions. Therefore, the dislocationsof the buffer layer may be effectively reduced by doping the impurityperiodically.

Further, in the first buffer layer 31, the doping concentration of thetransition metal is not less than the peak value of the dopingconcentration of the impurity. The transition metal forms a deep leveltrap in the buffer layer to capture the background electrons.

Further, the second buffer layer 32 is doped with a transition metal,and a doping concentration of the transition metal in the second bufferlayer 32 is less than the doping concentration of the transition metalin the first buffer layer 31.

Further, the doping concentration of the transition metal in the secondbuffer layer 32 decreases along a direction away from the substrate 1,so as to avoid a tailing effect caused by the transition metal, andprevent current collapse. A minimum doping concentration of thetransition metal in the second buffer layer 32 is not greater than 3E16cm⁻³, otherwise a deep level trap formed by the transition metal withthe excessively high doping concentration may cause impurity scatteringand reduce mobility.

Further, the semiconductor structure further includes an impurity dopedin the second buffer layer 32. A doping concentration of the impurity isnot greater than the doping concentration of the transition metal in thesecond buffer layer 32.

Further, the transition metal includes at least one of Ti, Cr, Mn, Fe,Co, Ni, Cu, Zn, Mo, Ag and Cd, preferably, Fe. The impurity is C.

Further, a thickness of the first buffer layer 31 is 0.01 μm to 5 μm. Athickness of the second buffer layer 32 is 0.05 μm to 5 μm.

In the embodiments, the semiconductor structure may further include thenucleating layer 2 disposed between the substrate 1 and the buffer layer3 to reduce dislocation density and defect density, and preventremelting.

The semiconductor structure may be applied to various device structures,such as high electron mobility transistor, high electron mobilitytransistor including a heterojunction formed by aluminum gallium indiumnitrogen and gallium nitride, high mobility triode including aheterojunction formed by aluminum nitride and gallium nitride, galliumnitride Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET),Light Emitting Diode (LED), photodetector, hydrogen generator and solarcell. For example, if the semiconductor structure is applied to a LEDdevice, a light-emitting structure may be manufactured on thesemiconductor structure. If the semiconductor structure is applied to aHEMT device, a heterojunction structure may be epitaxially grown on thesemiconductor structure, as shown in FIG. 4.

FIG. 4 shows a schematic structural diagram of a HEMT device configuredwith a semiconductor structure. The HEMT device includes a substrate 1,a nucleating layer 2, a buffer layer 3, a channel layer 4, a barrierlayer 5, a passivation layer 6, a gate electrode 7, a source electrode 8and a drain electrode 9. The buffer layer 3 includes a first bufferlayer 31 and a second buffer layer 32.

In the embodiment, the substrate 1 may be a Si substrate. In otherembodiments, the substrate 1 may also be a sapphire substrate or a SiCsubstrate.

In the embodiment, the nucleating layer 2 is made of AlN, the bufferlayer 3 is made of AlGaN, the channel layer 4 is made of GaN, and thebarrier layer 5 is made of AlGaN. 2DEG is formed at an interface betweenthe channel layer 4 and the barrier layer 5.

In the embodiment, the passivation layer 6 may include at least one ofsilicon nitride, silicon dioxide, aluminum nitride, aluminum oxide,aluminum nitride oxide.

In the embodiment, ohmic contact is formed by the source electrode 8,the drain electrode 9 and the barrier layer 5. Schottky contact isformed by the gate electrode 7 and the passivation layer 6.

In the embodiment, the first buffer layer 31 is co-doped with atransition metal and an impurity. A doping concentration of thetransition metal remains constant, and a doping concentration of theimpurity is modulated periodically. The doping concentration of thetransition metal is greater than the doping concentration of theimpurity. The second buffer layer 32 is doped with a transition metal. Adoping concentration of the transition metal in the second buffer layer32 is less than the doping concentration of the transition metal in thefirst buffer layer 31. The doping concentration of the transition metalin the second buffer layer 32 decreases along a direction away from thesubstrate 1.

Specifically, as shown in FIG. 5, a horizontal axis represents athickness of a semiconductor layer. An upper surface of the secondbuffer layer 32 is taken as 0 nm. The upper surface of the second bufferlayer 32 is a surface of the second buffer layer 32 away from thesubstrate 1. A vertical axis represents doping concentrations of dopingatoms. In the embodiment, a negative axis direction of the horizontalaxis refers to a direction of the channel layer. 0 nm to 600 nm in thehorizontal axis refers to the second buffer layer 32, 600 nm to 900 nmin the horizontal axis refers to the first buffer layer 31, and greaterthan 900 nm in the horizontal axis refers to the nucleating layer. Inthe embodiment, the first buffer layer 31 is doped with the transitionmetal Fe and the impurity C. A doping concentration of Fe remainsconstant at 1E18 cm⁻³. In the first buffer layer made of AlGaN, Fe formsa deep acceptor energy level, and forms electrical traps to capturebackground electrons. In addition, diffusion of free electrons in 2DEGtoward the substrate may also be effectively avoided. The dopingconcentration of C is varied periodically. A peak value of the dopingconcentration of C is 2E17 cm⁻³, and a valley value of the dopingconcentration of C is 2E16 cm⁻³. In the second buffer layer 32, thedoping concentration of Fe decreases gradually to 2E16 cm⁻³. Fe isstopped doping at the upper surface (0 nm) of the second buffer layer32. That is, the doping concentration of Fe decreases rapidly.

In technical solutions of the embodiments, by doping the transitionmetal in the first buffer layer of the semiconductor structure, the deeplevel trap may be formed to capture the background electrons. Inaddition, the diffusion of the free electrons toward the substrate mayalso be effectively avoided. By reducing the doping concentration of thetransition metal in the second buffer layer, a tailing effect may beavoided and current collapse may be prevented. By doping periodicallythe impurity in the buffer layer, the impurity may be as an acceptorimpurity to compensate the background electrons, and then aconcentration of the background electrons is reduced. By using theperiodic doping method, dislocations, caused by doping, in the bufferlayer may be effectively reduced.

It may be understood that although the specification is described inaccordance with the embodiments, not each of the embodiments onlyincludes one independent technical solution. This narration manner inthe specification is only for clarity. Those skilled in the art mayregard the specification as a whole, and technical solutions in variousembodiments may also be appropriately combined to form other embodimentsthat can be understood by those skilled in the art.

Also, unless otherwise required by context, singular terms shall includepluralities and plural terms shall include the singular.

The series of detailed descriptions listed above are only specificdescriptions of feasible implementations of the present application, andare not used to limit the protection scope of the present application.Any equivalent implementation or modification made within the technicaland spirit of the present application shall be included in theprotection scope of the present application.

What is claimed is:
 1. A semiconductor structure, comprising: asubstrate; a buffer layer disposed on the substrate; wherein the bufferlayer comprises a first buffer layer and a second buffer layer upwardfrom the substrate in turn, the first buffer layer is co-doped with atransition metal and an impurity, a doping concentration of thetransition metal remains constant, and a doping concentration of theimpurity is modulated periodically, the second buffer layer is dopedwith a transition metal, and a doping concentration of the transitionmetal in the second buffer layer is less than the doping concentrationof the transition metal in the first buffer layer, and the dopingconcentration of the transition metal is not less than a peak value ofthe doping concentration of the impurity in the first buffer layer. 2.The semiconductor structure according to claim 1, further comprising animpurity doped in the second buffer layer, wherein a dopingconcentration of the transition metal is not less than the dopingconcentration of the impurity in an upper surface of the second bufferlayer, and the upper surface of the second buffer layer refers to asurface of the second buffer layer away from the substrate.
 3. Thesemiconductor structure according to claim 1, wherein the dopingconcentration of the transition metal in the second buffer layerdecreases along a direction away from the substrate.
 4. Thesemiconductor structure according to claim 1, wherein a peak value ofthe doping concentration of the impurity modulated periodically is notless than 1E17 cm⁻³, and a valley value is not greater than 50% of thepeak value.
 5. The semiconductor structure according to claim 1, whereina valley value of the doping concentration of the impurity modulatedperiodically is not greater than 5E16 cm⁻³ or 3E16 cm⁻³.
 6. Thesemiconductor structure according to claim 1, wherein doping of theimpurity takes a thickness of 100 nm or 50 nm as a period.
 7. Thesemiconductor structure according to claim 1, wherein the dopingconcentration of the impurity in the buffer layer changes with thethickness to present a periodic modulation of one or a combination of arectangular shape, a trapezoid shape and a triangle shape.
 8. Thesemiconductor structure according to claim 1, further comprising anucleating layer disposed between the substrate and the buffer layer. 9.The semiconductor structure according to claim 8, wherein the nucleatinglayer is made of one of AlN, GaN and AlGaN.
 10. The semiconductorstructure according to claim 1, wherein a minimum doping concentrationof the transition metal in the second buffer layer is not greater than3E16 cm⁻³.
 11. The semiconductor structure according to claim 1, whereinthe transition metal comprises at least one of Ti, Cr, Mn, Fe, Co, Ni,Cu, Zn, Mo, Ag and Cd.
 12. The semiconductor structure according toclaim 1, wherein the impurity is C.
 13. The semiconductor structureaccording to claim 1, wherein a thickness of the first buffer layer is0.01 μm to 5 μm, and a thickness of the second buffer layer is 0.05 μmto 5 μm.
 14. The semiconductor structure according to claim 1, whereinthe substrate is made of at least one of semiconductor materials,ceramic materials and polymer materials, and further made of sapphire,silicon carbide, silicon, lithium niobate, silicon on insulator, galliumnitride and aluminum nitride.
 15. A manufacturing method for asemiconductor structure, comprising: providing a substrate; forming abuffer layer on the substrate; wherein the buffer layer comprises afirst buffer layer and a second buffer layer upward from the substratein turn, the first buffer layer is co-doped with a transition metal andan impurity, a doping concentration of the transition metal remainsconstant, and a doping concentration of the impurity is modulatedperiodically, the second buffer layer is doped with a transition metal,and a doping concentration of the transition metal in the second bufferlayer is less than the doping concentration of the transition metal inthe first buffer layer, and the doping concentration of the transitionmetal is not less than a peak value of the doping concentration of theimpurity in the first buffer layer.
 16. The manufacturing method for thesemiconductor structure according to claim 15, further comprising:doping an impurity in the second buffer layer; wherein a dopingconcentration of the transition metal is not less than the dopingconcentration of the impurity in an upper surface of the second bufferlayer, and the upper surface of the second buffer layer refers to asurface of the second buffer layer away from the substrate.
 17. Themanufacturing method for the semiconductor structure according to claim15, further comprising: forming a nucleating layer between the substrateand the buffer layer.
 18. The manufacturing method for the semiconductorstructure according to claim 15, wherein the doping concentration of thetransition metal in the second buffer layer decreases along a directionaway from the substrate.
 19. The manufacturing method for thesemiconductor structure according to claim 15, wherein a peak value ofthe doping concentration of the impurity modulated periodically is notless than 1E17 cm⁻³, and a valley value is not greater than 50% of thepeak value.
 20. The manufacturing method for the semiconductor structureaccording to claim 15, wherein a minimum doping concentration of thetransition metal in the second buffer layer is not greater than 3E16cm⁻³.